This invention relates to adhesion promoters containing silane and polar functionality, such as carbamate, thiocarbamate, and urea, and electron donor or acceptor functionality, and particularly to adhesion promoters for use in coatings and on substrates for electronic applications.
Adhesive compositions are used for a variety of purposes in the fabrication and assembly of semiconductor packages and microelectronic devices. The more prominent uses are the bonding of integrated circuit chips to lead frames or other substrates, and the bonding of circuit packages or assemblies to printed wire boards. Currently, lead frames are made of 42Fe/58Ni alloy (Alloy 42), copper, or silver- or palladium-coated copper, and wire boards of ceramic or laminate. Adhesives that have good performance for semiconductor packaging may, however, be deficient in adhesion to one or more of these substrates.
The addition of adhesion promoters would serve to correct this deficiency, but the commercially available adhesion promoters do not augment adhesion to all the substrates and the materials tend to volatilize significantly before the cure temperature of the adhesive is reached. Thus, there is a need for new adhesion promoters with enhanced reactivity and lower volatility than those currently commercially available.
This invention relates to adhesive or coating compositions containing adhesion promoters, and to the specific adhesion promoter compounds. The adhesion promoter compounds contain a silane functionality; a polar functionality, generally carbamate, urea, or thiocarbamate, to increase the adhesion normally promoted by the siloxane functionality; and an electron acceptor or electron donor moiety to react with other resins present in the adhesive composition.
The molecular weight of these compounds may readily be adjusted for a particular curing profile so that the compound does not volatilize during curing.
The adhesion promoters of this invention have the structure 
in which
m and n independently are 1 to 6, preferably 1 to 3, and more preferably 1;
R is a C1 to C6 alkyl group, or an aromatic or heteroaromatic ring or fused ring having 3 to 10 carbon atoms within the ring structure, in which the heteroatoms may be N, O, or S;
R1 and R2 independently are a linear or branched chain alkyl or alkyloxy group having 2 to 100 carbon atoms, which chain may have cyclic moieties,
X and Y are O, S or N(R3) with the proviso that X and Y may not both be O or S, and in which R3 is a C1 to C4 alkyl, preferably is hydrogen, methyl, or ethyl, and more preferably is hydrogen;
and E is an electron donating or electron accepting group.
Suitable electron acceptor groups are, for example, maleimides, acrylates, fumarates and maleates. Suitable electron donor groups are, for example, vinyl ethers, and carbon to carbon double bonds external to an aromatic ring and conjugated with the unsaturation in the aromatic ring.
The activity of the electron donor functionality other than the vinyl ether functionality can be increased by adding electron donating substituents on the aromatic ring, or decreased by adding electron withdrawing substituents. The activity can also be varied by steric interaction. An increase in the number or size of alkyl substituents on the carbon to carbon double bond conjugated with the aromatic ring or the carbon to carbon double bond of the vinyl ether group will decrease the reactivity. Preferably, any substituents on the carbon to carbon double bonds will be hydrogen, or will be hydrogen with methyl as only one of the substituents.
One method of preparation of the adhesion promoter compounds proceeds through a reaction between a first starting compound containing the electron donor or electron acceptor and the R2 group and a second starting compound containing the silane and the R1 group. The R1 and R2 groups will each contain a co-reactive functionality, such that the reactive functionality on the R1 group will react with the functionality on the R2 group. Examples of co-reactive functionalities are alcohol, thiol or amine, which would react with an isocyanate. The choice of reactants in practice will be determined by commercially available starting materials. In theory, the choice of reactants can be chosen by the practitioner to achieve the desired end compound, but in any case, the chemical linkage will be a carbamate, thiocarbamate, or urea linkage.
Examples of suitable starting materials containing the siloxane functionality are gamma-isocyanatopropyltriethoxysilane, gamma-amino-propyltriethoxysilane, gamma-aminopropyltrimethoxysilane, N-beta-(aminoethyl)-gamma-aminopropyltrimethoxysilane, triaminofunctional silane, bis-(gamma-trimethoxysilylpropyl)amine, N-phenyl-gamma-am inopropyl-trimethoxy-silane, N-beta-(aminoethyl )-gamma-aminopropylmethyldimethoxy-silane, and gamma-mercaptopropyltrimethoxysilane.
Examples of suitable starting materials containing an electron donor functionality are hydroxybutyl vinyl ether, cinnamyl alcohol, 1,4-cyclohexane-dimethanol monovinyl ether, 3-isopropenyl-xcex1,xcex1-dimethylbenzyl isocyanate, N-(6-hydroxyhexyl) maleimide and isoeugenol.
Examples of suitable starting materials containing an electron acceptor functionality are dioctyl maleate, dibutyl maleate, dioctyl fumarate, dibutyl fumarate, and maleimides.
The adhesion promoters are formulated into adhesive, coating, potting or encapsulant compositions. The formulations typically will contain a curable resin one or more curing agents, and may contain a conductive or nonconductive filler, in addition to the adhesion promoter.
In general the silane adhesion promoters will be present in such compositions in an amount ranging from 0.005 to 15.0 weight percent of the composition.
Curable resins are many and varied and well-known to practitioners in the adhesive, coating, potting and encapsulant arts, and can be chosen by the practitioner to meet a specific end use.
Exemplary curing agents are thermal initiators and photoinitiators present in the adhesive composition in an amount of 0.1% to 10%, preferably 0.1% to 3.0%, by weight of the electron donor compound. Preferred thermal initiators include peroxides, such as butyl peroctoates and dicumyl peroxide, and azo compounds, such as 2,2xe2x80x2-azobis(2-methyl-propanenitrile) and 2,2xe2x80x2-azobis(2-methyl-butanenitrile). A preferred series of photoinitiators is one sold under the trademark Irgacure by Ciba Specialty Chemicals. In some formulations, both thermal initiation and photoinitiation may be desirable, for example, the curing process can be started by irradiation, and in a later processing step curing can be completed by the application of heat to accomplish the thermal cure.
In general, these compositions will cure within a temperature range of 70xc2x0 C. to 250xc2x0 C., and curing will be effected within a range of ten seconds to three hours. The time and temperature curing profile of each formulation will vary with the specific electron donor compound and the other components of the formulation, but the parameters of a curing profile can be adjusted by a practitioner skilled in the art without undue experimentation.
Suitable conductive fillers are carbon black, graphite, gold, silver, copper, platinum, palladium, nickel, aluminum, silicon carbide, boron nitride, diamond, and alumina. Suitable nonconductive fillers are particles of vermiculite, mica, wollastonite, calcium carbonate, titania, sand, glass, fused silica, fumed silica, barium sulfate, and halogenated ethylene polymers, such as tetrafluoroethylene, trifluoroethylene, vinylidene fluoride, vinyl fluoride, vinylidene chloride, and vinyl chloride. When present, fillers will be in amounts of 20% to 90% by weight of the formulation.